Hydroforming process



Sept. 1, 1959 A. WELTY, JR

HYDROFORMING PROCESS Filed Dec. 28, 1955 Albert B. Wehy, Jr. I lnvetorByj' Attorney United States Patent 2,902,427 HY DRQFORNDNG PROCESSAlbert B. Welty, Jr., Westfield, NJ., assignor to Esso Research andEngineering Company, a corporation of Delaware Application December 28,1955, Serial No. 555,885 l 7 Claims. (cl. 208;'65)

The present invention relates to improvements in hydroforming. Moreparticularly, the present invention relates to the hydroforming of thenaphtha in the presence of platinum in a fixed bed type of operation inwhich process the total naphtha is fractionated to obtain a low boilingfraction boiling up to 200 F. and a higher boiling fraction boilingabove 200 F. and separately treating the said fractions under conditionswhich give improved results.

Hydroforming is a process in which a naphtha is treated in the presenceof a solid catalytic material and hydrogen at `elevated temperatures andpressures with the result that the naphtha is improved in octanequality. The principal reaction during hydroforming is thedehydrogenation of naphthenes present in the feed to the correspondingaromatics. There is also some isomerization of normal paraihns to formisoparaiiins as well as isomerization of alkylated cyclopentanes tocyclohexanes and some hydrocracking of the higher boiling paraflins tolower boiling products. As ordinarily carried out, the process resultsin the net production of hydrogen but in any event there is no netconsumption of hydrogen.

It is now a matter of record and commercial practice in this country tohydroform naphthas in order to produce high quality aviation gasolineand motor fuel. The catalyst employed in hydroforming may be in the formof fixed beds or the caalyst, in powdered form, may be employedutilizing the uidized solid technique. At the present time the catalystsprincipally in commercial use are platinum `carried on alumina, ormolybdenum oxide carried on alumina, the former being used in the formof fixed beds in a multi-stage operation with reheating between stages,while the latter is being employed in the form of a uidized bed.

In hydroforming naphthas the optimum pressure is different for variousboiling range naphthas. In general, high boiling naphthas are treated atmoderately high pressures for best results. The lower boiling naphthas,on the other hand, and in particular, the naphtha fractions boilingbelow 200 F. are treated at fairly low pressures for best results.

These phenomena are due to the fact that the high hydrogen partialpressure characteristic of the high pressure operation tends to preventformation of aromatics from parans and dimethylcyclopentanes, which arethe principal constituents of all virgin napthas boiling below 200 F.These naphthas may contain some benzene and cyclohexane, but thequantity present is usually quite small. On the other hand, mostnaphthas, boiling above 200 F. and say up to 300 or 400 F., arerelatively rich in cyclohexane homologues such as methyl cyclohexane,dimethylcyclohexane, etc. All cyclohexane homologues are very readilyconverted into aromatics by dehydrogenation at normal hydroformingtemperatures even at very high pressures, like 400-600 p.s.1.

It is clear from this that higher operating pressure,

ceN

2 which results in higher hydrogen partial pressure, can be used on thehigh boiling feeds than on the low boiling feeds.

The rate of deactivating coke formation on the catalyst determines thelength of time it may be used before regeneration is required and alsothe catalyst life or the length of time the catalyst may be employedbefore it is required to replace it and, therefore it is desirable tominimize this coke formation. It is common knowledge that the higher thehydrogen partial pressure, the lower the rate of coke formation will be.Therefore, higher pressure operations are required to produce aromaticsin good yields with minimum coke formation and longer catalyst life. Theoptimum operating pressure for high boiling naphthas such as thoseboiling above 200 F. will be considerably higher than that for lowboiling naphthas such as particularly those boiling below about 200 F;

The object of the present invention, therefore, is to hydroform lightnaphtha and heavy naphtha separately in the same equipment under optimumconditions for each. The present invention provides means whereby thiscan be accomplished.

In a hydroforming plant designed for hydroforming at say 400 p.s.i.g.,if the pressure were to be reduced to say 200 p.s.i.g. during thetreatment of the light naphtha, the recycled gas rate (the standardcubic feet of hydrogen containing gas feed to the reaction zone witheach barrel of naphtha feed) would be greatly reduced because of thegreater pressure drop through the system.

Since one is desirous of reducing hydrogen partial pressure anyway, thisgreatly reduced recycle gas rate would not be harmful from thestandpoint of the reaction itself. However, from the practicalstandpoint, this is a very serious problem. The hydroforming reaction ishighly endothermic, that is, a large amount of heat is consumed when thereaction occurs. The catalyst is disposed in one or more reactors inseries and each reactor runs adiabatically, that is, no heat is put intoor taken out of each reactor. Because of the large heat absorption bythe reaction, there is a large temperature drop from the reactor inletto outlet. This is undesirable because as the temperature drops, therate of reaction decreases, and, in fact, this is the reason why it isnecesessary to use more than one reactor in series and to reheat thehydrocarbon between reactors. The magnitude of this temperature drop isVery important in the hydroformer design. If the temperature drop isgreat, then a large number of reactors and reheat steps are required.This is expensive. If, on the other hand, the temperature drop is verysmall, only a few reactors with reheat are required.

The temperature drop for `a given amount of reaction depends solely onthe heat capacity of the vapors flowing through the bed. The higher theheat capacity, the lower the temperature drop will be. For this reason,it is desirable to recirculate as much recycle gas as practical from thestandpoint of pressure drop through the system, compresso-r horsepowerrequired, size of heat exchangers required, etc. With a recycle gasrate, for example, of 6,000 s.c.f./bbl. of feed, the recycle gasactually has more heat-absorbing capacity than the feed itself. In thiscase, depending somewhat on the nature of the feed stock and severity ofreaction, the 6,000 scf/bbl. of recycle gas might have a heat capacityof about 180 B.t.u.s per F. whereas the barrel of feed would have a heatcapacity of about B.t.u.s/ F.

Modifying operating conditions, such as by reducing pressure, so thatthe recycle gas rate is sharply reduced, the .heat absorbing capacity ofthe vapors passing through the bed will be much reduced and, therefore,the temperature drop will be very much increased for a given amount ofreaction. In practice, what would really happen is Vthat the temperaturewould-get so low that the same amount of reaction could no longerbeeffected. ThisV means either that-the octane number and amount ofconversion of the feed will be much reduced 'orthat the naphthafeed rateto 'the unit must be reduced.vr

vAsrpointed out previously," however, it is 'desirable to be'able tohydroform bo'th 'heavy and very light feed stocks in the same unit'atconditions approximating Vthe optimum for each. Optimum conditionsforthe relatively low boiling' feed 'require much lower hydrogen partialpressure than for the higher boiling feedstock. However, when thepressure is `reduced in a unit designed'fo'r Ahigh pressure operation onthe high boiling feeds, "one can no longer maintain the vrecycle 'gas'rate necessary to provide the necessary heat-carrying capacity for thevapors as they pass through the bed. n

Theoretically, it would be possible to provide additional compressorcapacity so as simply to overcome the higher pressure drop caused by thehigher velocities when roperating at low pressures. Depending onconditions, this might require from two to five times as much compressorcapacity and, furthermore, the pressure drop through the catalyst bedswould beveryV high. The high pressure drop through the catalyst beds isundesirable becausethe catalyst is crushed and reduced in size.

The heat carrying capacity ofthe recycle gas depends -on'the gases ofwhich it is composed. On a volumetric basis, hydrogen, which is theprincipal volumetric component, has a very low -heat capacity, `whereasa hydrocarbon, like butane, for example, Vhas a relatively high -heatcapacity. The volumetric heat capacity of fbutane gas is approximatelyfour times as high as that of hydrogen. The reason for this is thegreaterweight of butane `per unit volume 'of gas as compared tohydrogen. Recycle gas is a mixture of many gases-its 'principalcomponent is hydrogen but it also contains substantial quantities ofsaturated hydrocarbons. Generally, it contains, on a volumetric basis,more methane than ethane, more ethane than propane, more propane thanbutane, etc. Usually, relatively little C6 or C7 hydrocarbons arepresent. Y

One way to increase the heat carrying capacity of this recycle gas thenis to reduce rits hydrogen content and at the same time increase thecontent of highermolecular weight hydrocarbons, particularly Cs, Cs,Css, etc. Usually, the hydroformed product is cooled toa `temperature ofabout 100 F. and thereafter the gas and liquid separated. This gas isthe product gas and a portion of it is also the recycle gas. Thecomposition of the recycle gas depends upon the quantities of gaseousmaterials being produced, to some extent on the nature of the liquidproduct, and very much upon the temperature and pressure of liquid-gasseparation. To increase the recycle `gas heat carrying capacity, theproduct may be cooled not to the conventional 'temperature of about 100E., but to some higher temperature, say .tofabout 300 F. The followingtable shows the eifect of separator temperature on the specic gravity ofthe recycle gas and its heat carrying capacity, lin `a particular case.

l Standard cubic feet.

Thus, by separating at a 300 F. separator temperature instead of 100 F.,one Vcan use a recycle gas rate 0.028+0.065=42% as greatv and have thesame temperaturedrop through the reactor system for the same total heatof reaction.

Since the main object ofthe present rinvention.is-.to

, `4 reduce the hydrogen partial pressure for light naphtha hydroformingby reducing pressure, this reduced hydrogen concentration in the recyclegas actually helps to attain the optimum condition for this lightnaphtha operation.

It will thus be seen that by means of varying the separator temperature,it ispossible to vary the hydrogen partial pressure substantiallywithout any change in the total pressure whatsoever. In actual practice,however, it :is preferable not vonlyto .increasefthe separatoritemperature `when lower hydrogen partial pressure is desired, but toreduce pressure at the same time. There are two reasons for this. Thefirst is that thermal cracking reaction is encouraged by the use ofVhigher pressures. Since thermal cracking produces Aa greater proportionof gas and does not increase the octane number as much as the catalytichydroforming reaction, the use of higher pressure results in slightlylower yields. Therefore, the combination of reducing pressure andraising separator temperature when running on light'feed stocks willgive higher yields than the operationwhere pressure is not decreased butseparator temperature is raised sufficiently to give the same hydrogen`partial pressure. Another practical reason for preferring thecombination of decreasing, pressure and raising separator temperaturehas to do with the recycle gas compressor. Suppose, for example, thatvone were operating at a pressure such that the suction pressure on thecompressor is 350 p.s.i.g. when .hydroforming higher boiling 'feedstocks and using a'separator temperature of about F. `Now suppose oneraises vthe separator temperature without changingthecompressor suctionpressure. The lchange in gas composition'increases the horsepowerrequirement of the'compressor so that the compressor and the kmotorthatdrivesrit have to be capable `of handling this Vgreaterenergyrequirement. The reason this vhorsepower requirement'increases hastodo with the increased density'of the recycle gas which it Aiscompressing. While it is quite possible to design the compressor and itsdriver to handle this higher load, thisfdoes increase their cost verysubstantially. By reducingv the `suction pressure on the lcompressorbyreducing the overall pressure on the system, one can maintain thehorsepower requirement ofthe compressor essentially constant even whilelone raises thesseparator temperature to increasev its density.

The manner -of operating, outlined .above, would vresult in importanteconomic advantages over a system in which-merely `the total pressure isdecreased during fthe treatment of the low boiling naphthaconstituentsbccausethe reheat furnaces 'and thecompressors would beutilized .at al1 times to the full extent vof their Arespective designedcapacities. i

In the accompanying `drawing therefis lset forth diagrammatically vanapparatus layout :in whicha preferred modification of the: presentinvention may .be carried into effect.

Referring yin `detail to thesdrawing, naphtha feed l"is introduced Itothe present system .through line '.1. '-'The naphtha is heated infurnace and thence withdrawn in vapor formvia line 4 and ycharged toa'separator or fractional distillation column V5, wherein a yfractionboiling from-Oto 200 P is 'withdrawn overhead throughline 6 and chargedto a storage-drum 7, while va fraction boiling vfrom 200 F. 'to`say"400or F. is-withdrawn' as Ibottoms `from column 5, lineS andchargedtov a heavy naphtha storage ldrum 9. As will subsequently appear thehydroforrning of the naphtha is ina .blockedV type-ofV -operation, thatyis vto say, the :heavy naphtha land the light naphtha are separatelyprocessed. Toward thisend, therefore, While the light naphtha remainsVin storage in 'tank 7 the heavy naphtha is withdrawnfrorn-tank throughvalvedline 10 and charged toa furnace 111. 'Simultaneyousl-y recycledgas obtained from Ythe'product recovery system, as will subsequentlyappear, is passed via linez12 into line 1Q and, therefore, heatediinfurnace 1'51` withlthe heavy naphtha feed to hydroforming temperatures.This heated mixture is thence Withdrawn from furnace 11 through line 13and charged to the first reactor 14 of a series of reactors. The mixtureof heavy naphtha vapors and hydrogen-containing gas passes throughreactor 14 in contact with a bed of catalyst C at conditions oftemperature and pressure and residence time as hereinafter more fullyspecified with the result that the naphtha undergoes at least partialhydroforming. Due to the fact that the reaction is highly endothermicthere is subsequently a temperature decrease from the inlet to theoutlet of reactor 14 so that product withdrawn via line 15 is reheatedin the second furnace 16, withdrawn from said furnace and thence passedvia line 17 to a second reactor 18 Where again the naphtha contacts abed of catalyst C and undergoes further hydroforming. The product iswithdrawn from reactor 18 via line 19 and is reheated in a third furnace20, withdrawn through line 21 and charged to a third reactor 22 alsocontaining a bed of catalyst and wherein the hydroforming reaction issubsequently completed. The product is withdrawn from reactor 22 throughline 23, cooled in 24 to a temperature of about 100 F thence withdrawnthrough line 25 and charged to a separation drum 26. From separationdrum 26 recycled gas is recovered overhead via line 27, forced through acompressor 28 and charged via line 12 to line 10, as previouslyexplained. Excess recycled gas may be ejected through line 33. Thehydroformed product is withdrawn from separator 26 through line 30,passes through valve 37, line 32 and valve 42 to a conventionalstabilizing and rerunning system.

In treating the light naphtha under a pressure substantially lower thanthat maintained during the treatment of the heavy naphtha, the ow ofheavy naphtha from storage drum 9 is discontinued and light naphtha iswithdrawn from storage drum 7 via valved line 34. It is mixed withrecycled gas obtained via line 12 and line 12a and charged to furnace 11wherein the mixture is heated to reaction temperatures and this mixtureis then passed through the series of reactors in the same manner as thatpreviously described in connection with the processing of the heavynaphtha with the exception that, as previously pointed out viz., thatthe system is now operated at a substantially lower pressure and theseparator drum 26 is operated at a substantially higher ternperature bycontrolling the degree of cooling in cooler 24 so that the recycled gasrecovered overhead from separator 26 via line 27 is at a substantiallyhigher temperature than that at which the recycled gas exists whenprocessing the heavy naphtha. Product gas for recovery leaves separator26 through line 29, passes through valve 3S and line 39 to cooler 38.Liquid product passes from the bottom of separator 26 through line 30through valve 36 and line 40 where it combines with the product gas andpasses through cooler 38. Here gas and liquid are cooled to conventionaltemperatures suc'h as 100 F. and then separated again in vessel 31. Gasproduct leaves through line 33 and pressure control valve 31 and passesto a conventional gas recovery system. Liquid product leaves separator31 through line 32 and valve 42, which controls the level in separator31, and passes to a conventional liquid stabilizing and rerunningsystem.

The operation described above is completely self-contained. However, itis obvious that the desired increase in recycle gas density and decreasein hydrogen concentration can be augmented by the use of heavy gaseoushydrocarbons such as propane, butane, pentane, etc., from an extraneoussource. When this is desired, these gases can be introduced to therecycle gas system through line 43 and valve 44. In the latter case theraw product may be cooled to about 100 F. in 24.

In order to more fully explain the present invention, the followingspecific example is set forth. A naphtha having the following inspectionwas processed in the manner set forth immediately below with the resultsshown.

Inspection:

Boiling range (total naphtha), F 152-387 Naphthenes, vol. percent 43Parans, vol. percent i 49 Aromatics, vol. percent 8 Bromine number 0.2Sulfur, wt. percent 0.005 Octane number, CFRR 55.7

Conditions in reactor 14 during processing of heavy naphtha:

Catalyst composition- 0.6 wt. percent Pt 0.6 Wt. percent Cl 98.8 wt.percent eta alumina Inlet temperature, F. 948 Pressure, p.s.i.g 420Residence time, sec. 5.8

Recycle gas feed to reactor, s.c.f./bbl. oil 6000 Density of recycle gasrelative to air 0.25 Concentration of H2 in recycled gas, mol

percent In reactor 18 and 22 the catalyst is the same, the pressures aresubstantially the same (except for the pressure drop involved), theamount of recycled gas in reactor 18 and 22 respectively will beincreased somewhat due to the formation of hydrogen and the inlettemperatures of the feed to the reactors 18 and 22 respectively will besubstantially the lsame as the inlet temperature to reactor 14.

Condi-tions in reactor 14 during processing of light naphtha:

Catalyst composition- 0.6Awt. percent Pt 0.6 wt. percent Cl 98.8 wt.percent eta alumina Temperature maintained in separator 26, F.

Inlet temperature, "F 965 Pressure, p.s.i.g 256 Residence time, sec.12.1 Recycle gas feed to reactor, s.c.f./bbl. oil 2280 Density ofrecycle gas relative to air 0.96 Concentration of H2 in recycle gas 62Temperature maintained in separator 26,

The light and heavy naphtha hydroformates were combined and inspectedIWith the below results.

It will be understood that the foregoing example is illustrative of -theinvention but does not impose any limitation thereof. `Good results areobtainable by operating within the following ranges.

Conditions during heavy naphtha hydroforming:

Catalyst-Platinum or palladium suitably supported. Inlet temperature, F.900-1000 Pressure, p.s.i.g 350-600 Residence time, sec 4 20 vRecycle gasfeed to reactor, s.c.f./bb1.

Density of recycle gas relative to air 0.l-().4 `Concentrationf.H2-1'-nr.ecycled gas 70-95 Temperature ,maintained :in `separator i26,

Conditions duringligh-t naphtha hydroforming: YCatalyst-Plati'num orpalladium suitably supported.

Inlet temperature, `F. 900-1000 Illressure, p-.s.i.g 50-300 Residencetime, sec. 8-25 Recycle gas feed to reactor, .sl.c.f./bbl.

oil `150G-3000 Density of recycle gas relative .to air 0.401.0Concentration of H2 in recycle ,gas 55-75 Temperature maintained inseparator 26,

`In ordento recapitulatebrieily, the present invention contemplateshydroforming anaphtha in the presence of a platinum Vgroupmetal catalystdisposed in a plurality of reactors in which the naphtha is hydroformedby passage through the said reactorsin series vunder hydroformingconditions of temperature, pressure and contact time. -T he Ainventionis primarily characterized in that the Anaphtha is separated into aylight boiling fraction and a high boiling fraction and the separatedfractions are separately hy'droformed. 'The light naphtha is hydroformedunder substantially -lower pressure than the heavy naphtha but in orderto make full use of the heating and compres- `sor capacity the recycledgas fed to the reaction zone with the low boiling or light naphthacontains a higher percentage of hydrocarbons than does the recycled gasemployed in the heavy naphtha. It is thus necessary to so operate thehydroforming of the .light naphtha that the recycled gas will contain atleast 50% of the heat necessary to support the endothermic reaction ofhydroforming. Thus additional .hydrocarbons over and above that normallyobtained from the product separation drum lfor recycling is attained byoperating the said separation drum at a higher temperature than.normally employed and also adding gaseous hydrocarbons leither from eX-traneous sources of from the finishing ofthe raw hydroformate itself.

Numerous modifications of the invention will be apparent to those whoare familiar Iwith this artlwithout departing from the spirit thereof.

What is claimed is:

1. In an adiabatic blocked naphtha hydroforming proces-s carried out inthe presence of a platinum group metal catalyst and added hydrogen under-hydroforming conditions of temperature, ,pressure and residence time ina system, the improvement which comprises separating the .feed naphthainto va fraction boiling below 200 F. and a second fraction boilingabove about 200 F. alternately .treating the separated fractions in thesame system under hydroforming conditions, characterized in that (l) theIlower boiling fraction is treated under a relatively low hydrogenpartial pressure, (2) under a Vlower total pressure land alower recycle-gas rate than said higher boiling fraction, and (3) in which thehydrogen-containing recycle, gas fed toV the .reaction zone during thehydroforming of the said lower boiling fraction possesses a heatcapacity substantially greater than the said hydrogen-containing gas fedto the system during the hydroforming of said higher boiling fractiondue to the inclusioin, in said hydrogen-containing recycle gas fed tothe system during hydroforming of the lower boiling fraction of. ahigher volumetric percentage of hydrocarbons than contained in thehydrogen-containing recycle gas fed to the hydroforming zone during lthehydroforming of the said higher boiling naphtha caused by separating thesaid hydrogen-containing recycle gas from the product obtained byhydroforming the said lower boiling fraction ata temperature of fromabout '200 to 325 F., whereby increased quantities of aromatics areformed from paratlins-present 1in the said low boiling naphtha feed,furthercharacterized in that the energy requirements for circulating thesaid hydrogen-containing recycle :gas to the lhydroformingtreatment ofthe lower boilingfractionY is substantially the same as the energyrequirements for circulating recycled gasto the hydroforming treatmentof the higher lboiling fraction.

2. .The method set forth in claim 1 in which extraneous hydrocarbonsxareadmixed with the hydrogen-containing lgas fed to the hydroforming.zone'during the hydroforming of said low boiling naphthas to reduce thehydrogen partial pressure `of the said hydrogen-containing gas and atthe same time to increase the heat capacity of said hydrogenfcontaininggas.

3.V Animproved process for hydroforming a naphtha containing .both highand low boiling naphtha fractions in a'system comprising a plurality ofreactors, each containing a platinum group metal catalyst characterizedin that the naphtha is passed in series, together with ahydrogen-containing recycle gas, through the several reactors in contactwith the said catalyst, the improvement resulting in .producing ahydroformed product Vof improved octane rating in increased yield due atleast in part to an increased yield of aroma-tics formed from parafnichydrocarbons in the said low boiling fractions which comprisesseparating the naphtha into a 10W boiling fraction and a ln'gh boilingfraction, separately hydroforming .the said .fractions in the saidsystem at elevated temperatures and under -elevated pressures, the saidfraction containing the low boiling naphtha fractions being hydroformedunder a hydrogen partial pressure lower than that existing Aduring thehydroforming of the high boiling naphtha fractions, furthercharacterized in that the rate at which the `hydro,gen-containing .gasis fed to the system during the low boiling naphtha treatment issubstantially `less/than when the high boiling fractions are undergoingtreatment, recovering raiw products from .the respective treatments,cooling the raw products to condense normally liquid constituents,recovering a hydrogen-containing gas from both treatments for recycle tothe process and causing an increase in the heat carrying capacity of thehydrogen-containing recycled gas for use during the treatment of the lowboiling hydrocarbon fractions by separating the said hydrogen-containinggas from tihe low boiling hydroformed liquid product at a temperature offrom about 200-300 F., further characterized in that the energyrequirements for circulating the said hydrogen-containing recycle gas tothe hydroforming treatment of the lower boiling fraction issubstantially the same as the energy requirements for circulatingrecycled gas to the hydroforming treatment of the higher boilingfraction.

4. The lmethod set foith in claim 1 in which the energy requirements forrecycling `the hydrogen-containing gas is maintained substantiallyconstant for both treatments by hydrofonning the light hydrocarbonfractions under a total pressure substantially lower than that existingin the reaction zones during the hydroforming of the higher boilingnaphtha fractions.

5. The method set forth in claim 3 in which the hydroforming is carriedout in the presence of a catalyst containing platinum.

6. The method set forth in claim 3 in which the said low boilingnaphthas comprise a fraction boiling in the range of from about 0`200 F.

7. The method set forth in claim 4 in which the pressure maintainedduring the hydroforming of the lower boiling hydrocarbon fractions isfrom about 50 to 300

1. IN AN ADIABATIC BLOCKED NAPTHA HYDROFORMING PROCESS CARRIED OUT INTHE PRESENCE OF APLATINUM GROUP METAL CATALYST AND ADDED HYDROGEN UNDERHYDROFORMING CONDITIONS OF TEMPERATURE, PRESSURE AND RESIDENCE TIME IN ASYSTEM, THE IMPROVEMENT WHICH COMPRISES SEPARATING THE FEED NAPHTHA INTOA FRACTION BOILING BELOW 200*F. AND A SECOND FRACTION BOILING ABOVE200*F. ALTERNATELY TREATING THE SEPARATED FRACTIONS IN THE SAME SYSTEMUNDER HYDROFORMING CONDITIONS, CHARACTERIZED IN THAT (1) THE LOWERBOILING FRACTION IS TREATED UNDER A RELATIVELY LOW HYDROGEN PARTIALPRESSURE, (2) UNDER A LOWER TOTAL PRESSURE AND A LOWER RECYCLE GAS RATETHAN SAID HIGHER BOILING FRACTION, AND (3) IN WHICH THEHYDROGEN-CONTAINING RECYCLE GAS FED TO THE REACTION ZONE DURING THEHYDROFORMING OF THE SAID LOWER BOILING FRACTION POSSESSES A HEATCAPACITY SUBSTANTIALLY GREATER THAN THE SAID HYDROGEN-CONTAINING GAS FEDTO THE SYSTEM DURING THE HYDROFORMING OF SAID HIGHER BOILING FRACTIONDUE TO THE INCLUSION, IN SAID HYDROGEN-CONTAINING RECYCLE GAS FED TO THESYSTEM DURING HYDROFORMING OF THE LOWER BOILING FRACTION OF A HIGHERVOLUMETRIC PERCENTAGE OF HYDROCARBONS THAN CONTAINED IN THEHYDROGEN-CONTAINING RECYCLE GAS FED TO THE HYDROFORMING ZONE DURING THEHYDROFORMING OF THE SAID HIGHER BOILING NAPHTHA CAUSED BY SEPARATING THESAID HYDROGEN-CONTAINING RECYCLE GAS FROM THE PRODUCT OBTAINED BYHYDROFORMING THE SAID LOWER BOILING FRACTION AT A TEMPERATURE OF FROMABOUT 200* TO 325*F., WHEREBY INCREASED QUANTITIES OF AROMATICS AREFORMED FROM PARAFFINS PRESENT IN THE SAID LOW BOILING NAPHTHA FEED,FURTHER CHARACTERIZED IN THAT THE ENERGY REQUIREMENTS FOR CIRCULATINGTHE SAID HYDROGEN-CONTAINIG RECYCLE GAS TO THE HYDROFORMING TREATMENT OFTHE LOWER BOILING FRACTION IS SUBSTANTIALLY THE SAME AS THE ENERGYREQUIREMENTS FOR CIRCULATING RECYCLED GAS TO THE HYDROFORMING TREATMENTOF THE HIGHER BOILING FRACTION.